The present inventions relates to a manufacturing method of batteries.
So far, secondary batteries for instance such as non-aqueous solvent type batteries are in broad use as a power source for portable telephones, video cameras or the like. In batteries for power source, as the aforementioned instruments become smaller in size and higher in performance, demands on smaller size, lighter weight, higher voltage, larger capacity and so on are increasingly stronger. Corresponding to these demands, in for instance Japanese Patent Laid-open Application Nos. HEI 3-230474, HEI 3-225765 and so on, polymer batteries of approximately 1 mm thickness are disclosed.
That is, in these batteries, a battery element, after aligning to accommodate in an envelope film body (exterior envelope body/bag body) having one open-end, is wrapped therewith. Then, from the opening thereof a prescribed electrolytic solution is injected. Thereafter, the opening is hot-melted to constitute a hermetic-sealed battery. In manufacturing the above battery, there is another method where after sandwiching the battery element by the envelope film and folding together the film with the battery element inside thereof, opposite peripheries of both sides of the film are mutually hot-melted to seal, resulting in formation of an enveloped body. Further, the battery element can be formed planar by pressing a cylindrically wound body.
FIG. 3 is a cross section showing a substantial constitution of a battery. Here, the battery element 1 comprises a positive sheet electrode 1a and a negative sheet electrode 1b, a sheet electrolyte 1c, a current collector sheet not shown in the figure, and a positive electrode terminal 1axe2x80x2 and a negative electrode terminal 1bxe2x80x2. The positive and negative sheet electrodes 1a and 1b are facing to each other. The sheet electrolyte 1c is hermetically interposed between the both electrodes 1a and 1b. The current collector sheets connect electrically to the electrodes 1a and 1b respectively. The positive electrode terminal 1axe2x80x2 and the negative electrode terminal 1bxe2x80x2 are separated from the current collectors of the positive and negative electrodes 1a and 1b. Here, the positive and negative electrode terminals 1axe2x80x2 and 1bxe2x80x2 are extended outside of an envelope film body 2.
The positive sheet electrode 1a is composed with lithium ion storing and ejecting lithium containing metal oxides (for instance, lithium manganese compound oxide, lithium containing cobalt oxide) or manganese dioxide as main constituents. The negative sheet electrode 1b is composed of lithium metal or lithium storing and ejecting carbonaceous material, and lithium alloy. The polymer electrolyte 1c is constituted by impregnating or charging ethylene carbonate solution of lithium salt that is non-aqueous electrolytic solution, in separator base material consisting of nonwoven fabric of polypropylene or the like.
These kinds of planar secondary batteries, compared with lead storage batteries and nickel-cadmium secondary batteries, can be made larger in capacity and lighter in weight. By contrast, there are the following inconveniences. That is, in the steps of manufacturing the batteries, after aligning and accommodating the battery element 1 in the envelope film body 2, a prescribed electrolytic solution is injected.
The reason for the inconveniences is as follows. As a battery is made larger in capacity, the battery element 1 is made finer to result in a decrease of a space for impregnating the electrolytic solution. That is, in order to improve a volume efficiency of a battery, a gap space inside of the envelope film body 2 is made as small as possible. However, reducing the gap space in the envelope film body 2 as small as possible invites a difficulty when the prescribed electrolytic solution is injected. As a result, there is a possibility that the prescribed amount of the electrolytic solution is not injected and is not held inside thereof, resulting in liability to invite fluctuation of battery performance and quality.
To avoid occurrence of such problems, a method has been adopted in which injection and impregnation of the electrolytic solution into the envelope film body 2 therein the battery element 1 is accommodated are repeated a plurality of times. However, a plurality of times of repetition of injection of the electrolytic solution results in an increase of the time needed to inject the electrolytic solution. As a result, due to evaporation of the component of the injected electrolytic solution or to accumulated error of the amount of injection caused by separated injection of the electrolytic solution, accuracy of, the amount of injection of the electrolytic solution is lowered.
The present invention is performed taking into account the above circumstances. The object of the present invention is to provide a manufacturing method of batteries that can not only make the batteries smaller and lighter but also can mass-produce the batteries of high reliability.
A present manufacturing method of batteries comprises the steps of:
accommodating a battery element in an envelope film body of which one end side is opened to form an opening for injecting electrolytic solution; and
sealing the opening after the electrolytic solution is injected through the opening of the envelope film body;
wherein the opening side of the envelope film body is made larger in shape and dimension than prescribed ones to form a temporary reservoir of an injected electrolytic solution and after a prescribed amount of the electrolytic solution is injected, a region of the prescribed shape and dimension is sealed and cut to form a battery.
In the above manufacturing method of batteries, in accommodating the battery element, a laminate film formed by disposing resin layers on both surfaces of a metallic layer can be used as an envelope film body.
In the above manufacturing method of batteries, the envelope film body can be sealed by hot-melting the hot-melt film disposed on a sealing region outside of at least the region of prescribed shape and dimension.
In the present invention, relative to the battery element, the opening side of the envelope film body of which one end is opened is made longer. The longer opening side, after utilizing as a temporary reservoir of the electrolytic solution during injection of the solution, is sealed and cut at a region of the prescribed shape and dimension. That is, in the manufacturing steps of the batteries, the opening side that is an opening through which the electrolytic solution is injected in the envelope film body is extended longer than a region to seal and cut at the final stage of production. The extended region of the envelope film body is utilized as an electrolytic solution reservoir (funnel). Thereby, without invoking to inconvenient operations and equipment, with high precision, a definite amount of electrolytic solution can be injected.
In the present invention, for the battery element, a laminate or a planar body can be cited. The laminate is formed by interposing an electrolyte sheet, which concurrently works as a separator of a battery, between the positive and negative sheet electrodes. The planar body is obtained by rolling a winding body in which the electrolyte sheet that concurrently works as a separator of a battery is interposed between the positive and negative sheet electrodes. That is, the battery element comprises a positive sheet electrode, a negative sheet electrode and a polymer-electrolyte system. The positive sheet electrode is formed by laminating a positive electrode containing an active material such as metal oxide, non-aqueous electrolyte and electrolyte holding polymer onto a current collector. The negative sheet electrode is formed by laminating a negative electrode containing an active material storing and ejecting lithium ions, non-aqueous electrolyte and electrolyte holding polymer onto a current collector. The polymer-electrolyte system (for instance, a system of polymer such as hexafluoro propylene-vinylidene fluoride copolymer, and an ethylene carbonate solution of lithium salt, which is a non-aqueous electrolytic solution) functions as a separator and holds the electrolyte.
Here, as the active materials for the positive sheet electrode, for instance lithium manganese compound oxide, manganese dioxide, lithium containing cobalt oxide, lithium containing nickel cobalt oxide and, lithium containing amorphous vanadium pentoxide, chalcogenide compounds or the like can be cited. For the active materials for the negative electrode, for instance, bisphenol resin, polyacrylonitrile, baked cellulose or the like, baked cokes and pitch can be cited. These can include natural or man-made graphite, carbon black, acetylene black, Ketjen black, nickel powder or the like.
For the polymer-electrolyte system, ones in which in polymer electrolytes such as hexafluoropropylene-vinyliden fluoride copolymer, polyacrylonitrile derivatives, polyethylene oxide derivatives or the like, one that is obtained by dissolving approximately 0.2 to 2 mol/l of lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium trifluoromethane sulfonate or the like in non-aqueous solvent for instance such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl-ethyl carbonate or the like is occluded can be cited.
For the current collector of the positive sheet electrode, for instance aluminum foil, aluminum mesh, aluminum expanded metal, aluminum punched metal or the like can be cited. For the current collector of the negative sheet electrode, for example copper foil, copper mesh, copper expanded metal, copper punched metal or the like can be cited.
In the present invention, the envelope film body for accommodating the battery element is opened at one end and formed in a bag of which at least sealing and melting portion are formed of hot-melt resin. That is, the envelope film comprises an opening at the one end thereof of which width and length are large enough to be capable of sealing/drawing out and accommodating each electrode terminal of the sheet battery element. The length thereof in a direction toward the opening is made longer than that of the ordinary one. The envelope film body may be previously formed in a bag. Instead, the envelop film can be folded together and the battery element is interposed therebetween while drawing out the electrode terminal, the opposing faces of the both sides of the envelope film being hot-melted to form into a bag in the process of assemblage.
For the films forming the envelope film body, for instance polyimide resin film, polypropylene resin film, a laminate formed by disposing layers of resin on both surfaces of a metallic layer for humidity resistance purpose can be cited. In forming these film materials into an envelope film body, or in hot-melting/sealing the envelope film body after injection of the electrolytic solution, a layer of hot-melt adhesive can be interposed between both sealing surfaces that are facing or at least both opposing sealing surfaces of the film can be preferably made in advance of layers of hot-melt resin.
According to the present invention, in the steps of manufacturing polymer batteries, a prescribed amount of electrolytic solution can be injected with ease and accuracy. Accordingly, batteries of high quality can be manufactured with high yield. That is, by utilizing part of the envelope film body as a reservoir of the injected electrolytic solution, after supplying the prescribed amount of electrolytic solution, even in the continuous manufacturing process, interruption and switching of operations are made unnecessary. Further, even if the region for injecting the electrolytic solution of such as the battery element is dense to invite a difficulty in impregnating the electrolytic solution, the impregnation at a reduced pressure can be implemented as it is. Accordingly, good productivity can be maintained and since the definite amount of injection of the electrolytic solution is possible, batteries of high quality can be provided.